In the measurement of fire weather and forest inflammability, now practiced regularly at more than 90 forest stations in northern Idaho and western Montana, it is necessary to use many methods that are peculiar to this work. Some of these methods are familiar to meteorologists, but few foresters have had any appreciable training in meteorology. Others are of such, recent development and so specially designed for forest protection that they are unknown to most meteorologists and are not yet taught in the schools of forestry or described in any textbooks. The information available on these methods is scattered through numerous bulletins, reports, and official letters of instruction. Much of this information is assembled in this circular for more convenient reference. It has been prepared specifically for use in the Northern Rocky Mountain Region; but much of the material presented may be of value in other regions.